Vacuum insulating glass (VIG) units typically include at least two spaced apart glass substrates that enclose an evacuated or low-pressure space/cavity therebetween. The substrates are interconnected by a peripheral edge seal and typically include spacers between the glass substrates to maintain spacing between the glass substrates and to avoid collapse of the glass substrates that may be caused due to the low pressure environment that exists between the substrates. Some example VIG configurations are disclosed, for example, in U.S. Pat. Nos. 5,657,607, 5,664,395, 5,657,607, 5,902,652, 6,506,472 and 6,383,580 the disclosures of which are all hereby incorporated by reference herein in their entireties.
FIGS. 1 and 2 illustrate a typical VIG window unit 1 and elements that form the VIG window unit 1. For example, VIG unit 1 may include two spaced apart substantially parallel glass substrates 2, 3, which enclose an evacuated low-pressure space/cavity 6 therebetween. Glass sheets or substrates 2, 3 are interconnected by a peripheral edge seal 4 which may be made of fused solder glass, for example. An array of support pillars/spacers 5 may be included between the glass substrates 2, 3 to maintain the spacing of substrates 2, 3 of the VIG unit 1 in view of the low-pressure space/gap 6 present between the substrates 2, 3.
A pump-out tube 8 may be hermetically sealed by, for example, solder glass 9 to an aperture/hole 10 that passes from an interior surface of one of the glass substrates 2 to the bottom of an optional recess 11 in the exterior surface of the glass substrate 2, or optionally to the exterior surface of the glass substrate 2. A vacuum is attached to pump-out tube 8 to evacuate the interior cavity 6 to a low pressure, for example, using a sequential pump down operation. After evacuation of the cavity 6, a portion (e.g., the tip) of the tube 8 is melted to seal the vacuum in low pressure cavity/space 6. The optional recess 11 may retain the sealed pump-out tube 8. Optionally, a chemical getter 12 may be included within a recess 13 that is disposed in an interior face of one of the glass substrates, e.g., glass substrate 2. The chemical getter 12 may be used to absorb or bind with certain residual impurities that may remain after the cavity 6 is evacuated and sealed.
VIG units with fused solder glass peripheral edge seals 4 are typically manufactured by depositing glass frit, in a solution (e.g., frit paste), around the periphery of substrate 2 (or on substrate 3). This glass frit paste ultimately forms the glass solder edge seal 4. The other substrate (e.g., 3) is brought down on substrate 2 so as to sandwich spacers/pillars 5 and the glass frit solution between the two substrates 2, 3. The entire assembly including the glass substrates 2, 3, the spacers/pillars 5 and the seal material (e.g., glass frit in solution or paste), is then heated to a temperature of at least about 500° C., at which point the glass frit melts, wets the surfaces of the glass substrates 2, 3, and ultimately forms a hermetic peripheral/edge seal 4.
After formation of the edge seal 4 between the substrates, a vacuum is drawn via the pump-out tube 8 to form low pressure space/cavity 6 between the substrates 2, 3. The pressure in space 6 may be produced by way of an evacuation process to a level below atmospheric pressure, e.g., below about 10−2 Torr. To maintain the low pressure in the space/cavity 6, substrates 2, 3 are hermetically sealed. Small high strength spacers/pillars 5 are provided between the substrates to maintain separation of the approximately parallel substrates against atmospheric pressure. As noted above, once the space 6 between substrates 2, 3 is evacuated, the pump-out tube 8 may be sealed, for example, by melting its tip using a laser or the like.
A typical process for installing the pump-out tube 8 in the hole or aperture 10, includes inserting a pre-formed glass pump-out tube 8 in an aperture/hole 10 that has previously been formed (e.g., by drilling) in one of the glass substrates 2. After the pump-out tube 8 has been seated in the aperture/hole 10, an adhesive frit paste is applied to the pump-out tube 8, typically in a region close to the opening of the hole 10 proximate an exterior surface of the glass substrate 2. As noted above, the pump-out tube may be sealed after evacuation or purging of the VIG cavity.
After evacuation of the cavity to a pressure less than atmospheric, sealing of the pump-out tube may be accomplished by heating an end of the pump-out tube that is used to evacuate or purge the cavity to melt the opening and thus seal the cavity of the VIG window unit. For example and without limitation, this heating and melting may be accomplished by laser irradiation of the tip of the pump-out tube.
It may also sometimes the case that the pump-out tube may not be properly seated in the hole formed in the glass substrate. As a result, the pump-out tube may lean or tilt to one side, and thus not be substantially perpendicular to the surface of the glass substrate in which the hole is formed. As a result, in situations where the pump-out tube is improperly seated and is at an undesirable angle with the surface of the glass substrate, it is difficult to properly seal the pump-out tube because the laser cannot consistently melt the tip of the pump-out tube due, for example, to differences in distance between various portions of the angled pump-out tube top and the laser source. Inconsistent melting of the top of the pump-out tube may result in incomplete sealing and thus air leakage, which may, depending on the quality of the seal, occur rapidly or more slowly over time. In addition, based on the degree of tilt or tipping of the tube, the laser could hit the tube wall instead of the top. If the laser hits the tube wall, the laser could potentially bypass the tube and hit the frit, which may damage the frit or cause undesirable outgassing into the cavity. Therefore, what is needed is a way to seat the pump-out tube in the hole to reduce the amount of tipping of the tube to be within an acceptable range. As discussed below, according to certain example embodiments, this may be achieved by providing hole geometries and dimensions that assist in reducing pump-out tube tipping.
To overcome drawbacks such as those noted above with respect to tipping of the pump-out tube, according to certain example embodiments, at least a portion of the hole in the glass substrate in which the pump-out tube is inserted may be constructed such that the glass hole has a diameter sized to provide sufficient support to hold the pump-out tube in a substantially vertical orientation upon insertion in the hole, and thereafter. For example, and without limitation, according to certain example embodiments, the hole in the glass substrate into which the pump-out tube is to be inserted may be sized, for example, and without limitation, such that an inside diameter of the hole is not substantially more than about 0.1 mm greater than an outside diameter of the pump-out tube, and it is further preferable that the pump-out tube end that is inserted into the hole be substantially even with (e.g., substantially flush with) the interior surface of the glass substrate. According to further example embodiments, the pump-out tube may not fully extend through the hole to be flush with the interior surface of the glass substrate, and may be left just short of the interior surface by a distance of, for example, and without limitation, up to about 0.1 mm from the interior surface. In any event, it is noted that it is undesirable for the pump-out tube to extend beyond the surface of the glass substrate and into the cavity of the VIG window unit. According to further example embodiments, the hole may include a larger diameter recess formed at an outer surface of the glass substrate. The larger diameter portion of the hole, according to certain example embodiments, may form a recess portion in which excess frit, for example, may accumulate as a result of the insertion process, such as, for example, described above in connection with certain example embodiments. According to further example embodiments, the depth of the recessed portion may be between about one-fourth to one-half the thickness of the glass substrate, and may more preferably be about one-third the thickness of the glass substrate. The diameter of the larger diameter portion of the hole, according to certain example embodiments, may be in a range of about slightly greater than 0.1 mm larger than an outside diameter of the pump-out tube up to 1.0 mm larger than an outside diameter of the pump-out tube. According to certain example embodiments, a hole having an acceptable configuration to achieve the foregoing may be constructed using, for example, and without limitation, a two stage drilling process wherein a first portion of the hole is drilled from an outer surface of the glass substrate to a predetermined depth using a first drill bit, and a second portion of the hole may be drilled from an inner surface of the glass substrate to a predetermined height using a second drill bit. According to certain example embodiments, the first portion is drilled to a depth of about one-third to one half of the depth of the hole (e.g., thickness of the glass substrate). The remainder of the hole is provided by drilling the second portion from below using a second bit. In embodiments in which a recessed portion is formed, the diameter of the first bit is larger than the diameter of the second bit.
In certain instances, it was found that the vacuum atmosphere could be degraded after heat sealing an end of the pump-out tube. In some instances the leakage was rapid, while in other cases, the leakage occurred over a longer period, such as, for example, over the course of several days. It was discovered that cracks in the pump-out tube at an area at or near an interface of the pump-out tube and frit substantially contributed to the loss of vacuum in the cavity of the VIG window unit. It was determined that in certain cases the heat used to seal the upper (or outer) end of the pump-out tube may be conducted through the pump-out tube glass to the frit, resulting in thermal shocking of the glass pump-out tube in the vicinity of the frit-tube interface due to, for example, the temperature differential between the frit and the glass tube, which caused cracking of the pump-out tube in the area of the frit interface between the pump-out tube and the frit material. As noted above, the temperatures required to melt the end of the pump-out tube are typically very high. Cracking of the pump-out tube at the frit interface was discovered to be a cause of air leakage that may compromise the vacuum of the VIG window unit. It has been further found that heat conduction is dependent on a length of the pump-out tube. In other words, it has been surprisingly found that if the distance between the frit used to adhere the pump-out tube in the hole, and the end of the pump-out tube subjected to heat sealing, such as, for example, by laser heating, is too short, the potential for heat conduction to the frit, and thus thermal shocking of the pump-out tube at the interface of the pump-out tube and the frit, is increased. Therefore, in certain instances, a length of the pump-out tube, and more particularly, a length between the top of the frit and the end of the pump-out tube that is to be heat sealed, is arranged to reduce the possibility of thermal shock, and thus reduce or substantially avoid cracking of the pump-out tube at the frit interface with the pump-out tube. It is also the case that the length of the pump-out tube may be shortened. The pump-out tube typically comprises glass and is fragile. The longer the tube, the more chances that exist for damaging the tube during subsequent manufacturing steps that may be employed to complete the VIG window unit. Thus, a balance can be struck between the overall length of the tube and the distance from the end of the pump-out tube and the interface of the pump-out tube with the frit material. It has been found that in certain example embodiments setting a distance between the outer frit interface with the pump-out tube (e.g., at the top of the bump/mound of frit on the tube) and an end of the tube to be heat sealed to be in a range of from about 4.5 to 6 mm, more preferably in a range of from about 4.8-5.5 mm and more preferably about 5.0 mm, may overcome problems noted above related to thermal shock during heat sealing. In addition, it has been found that this range of tube length above the frit interface is also acceptable in terms of not substantially increasing the possibility or probability of damage to the tube during subsequent manufacturing processes.
These and other advantages are provided by a vacuum insulated glass window unit comprising: a first substrate having a hole defined therein for receiving a pump-out tube, the hole having a diameter in a range of about 0.05 to 0.2 mm greater than an outer diameter of the pump-out tube and more preferably in a range of about 0.05 to 0.15 mm greater than an outer diameter of the pump-out tube, and even more preferably about 0.1 mm greater than an outer diameter of the pump-out tube.
Further advantages are provided by a vacuum insulated glass window unit comprising: a first substrate having a hole defined therein for receiving a pump-out tube and a frit inclusive paste, wherein when the pump-out tube and the frit inclusive paste are disposed in said hole, a portion of the frit inclusive paste forms a bump of frit inclusive paste proximate a top of the hole where the hole exits the first substrate and substantially surrounding a portion of the pump-out tube and having a height measured from a surface of the first substrate, wherein a difference between the height of the bump of frit inclusive paste and a height of the pump-out tube extending out of the hole is in a range of about 4.5 to 6.0 mm, or more preferably in a range of about 4.8 to 5.5 mm, and even more preferably about 5.0 mm.
These and other embodiments and advantages are described herein with respect to certain example embodiments and with reference to the following drawings in which like reference numerals refer to like elements, and wherein: